Process of curing chemically treated cellulosic fabric

ABSTRACT

A process of curing cellulosic fabrics, which have been impregnated with a cross-linking agent, utilizing the application of microwave energy to impart durable crease resistance thereto. During curing, the heat which is generated in the fabric by the microwave energy is preserved but the water vapor thus produced is permitted to escape. The resulting cured fabric is wrinkleresistant and also exhibits increased strength and abrasion resistance compared to the same fabric cured by heat alone.

United States Patent 1191 Englert et al.

[ 51 Nov. 12 1974 1 1, PROCESS OF CURING CHEMICALLY 'IRICA'IEI) CELLULOSIC FABRIC [75] Inventors: Robert D. Englert, Corona Del Mar;

Lester P. Berriman, Irvine, both of Calif.

[63] Continuation'in-part of Ser. No. 886,769, Dec. 19,

1969, abandoned. 1

[52] US. Cl...... 2/243 R, 8/116 R, 8/186, 8/187, 8/D1G. 12, 38/144, 117/9331 DH ['51] Int. Cl .2. D06m 15/58 [58] Field of Search 8/D1G. 12, 116.3, 116 R, 8/186, 187; 117/931 DH; 38/144; 2/243 7 [56] References Cited UNlTED STATES PATENTS 2,603,741 7/1952 Seigfreid et a1 117/93.1-DH 2,689,806 9/1954 Dalton et a1. 117/93.1 DH 2,366,347 1/1945 Millson 8/D1G. 12 2,730,481 1/1956 117/93.1 DH 2,865,790 12/1958 Buer 117/93.1 DH 2,974,432 Warnock etal. 8/1163 X 3,127,732 4/1964 Brown et a1. 8/1163 X OTHER PUBLICATIONS Alexander et a1, Melliand Textilberichte, V01. 33, February, 1952, pp. 163-166. Alexander et al., Melliand Textilberichte, Vol. 33, March, 1952, pp. 2292 30. Copson, D. A., Microwave Heating in Freeze-Drying, Electronic Ovens and Other Appliances," Air- Publishing, Westport, Conn., 1962, pp. 299-302 and 378-380.

Primary Examiner-George F. Lesmes Assistant Examiner-J. Cannon Attorney, Agent, or FirmLyon and Lyon 57 ABSTRACT A process of curing cellulosic fabrics, which have been impregnated with a cross-linking agent, utilizing the application of microwave energy to impart durable crease resistance thereto. During curing, the heat which is generated in the fabric by the microwave energy is preserved but the water vapor thus produced is permitted to escape. The resulting cured fabric is wrinkle-resistant and also exhibits increased strength and abrasion resistance compared to the same fabric cured by heat alone.

12 Claims, 3 Drawing Figures HOT A\ R $0M RCF.

MLCRO WAVE OVEN w War/ rd /V x A Zr 4 v 2 PATENIEDHBV 12 I974 MICRO WAVE EN NHCRO WAVE OVEN I 1 PROCESS OF CURING CHEMICALLY TREATED CELLULOSIC FABRIC This application is a continuation in part of our copending application, Ser. No. 886,769, entitled Process of Curing Chemically Treated Cellulosic Fabric, and of applications, Ser. Nos. 598,575 and 476, l 26, all now abandoned.

In the textile industry, processes have been developed for treating fabrics to impart a durable crease resistance thereto, which involve impregnating the fabric with an aqueous solution of a'polyfunctional agent capable of cross-linking the fibers, which solution may contain softeners and the like. The fabric is then dried and thereafter cured by the application of heat.

In US. Pat. No. 2,974,432 to Warnock et al., there is described a method of manufacturing garments of these crease-resistance fabrics wherein the fabric is initially treated with the aqueous solution of thermally reactive agents and softeners. The fabric is thereafter dried at a temperature which is lower than the curing temperature of the agent, and then manufactured into a garment. After the garment has been completed, it is pressed just as a finished garment is pressed. The garment is then passed through a heated oven (e.g. gas fired) within which a temperature range is established within ranges determined by the type of garment which is being treated, as well as the agent being cured. This temperature must, of course, exceed the curing temperature of the agent with which the garment is impregnated. However, the temperature varies with the weight of the fabric as well as with the number of folds which have been pressed.

While such processes provide garments having crease-retaining or wrinkle-resistance characteristics, as the wrinkle recovery or crease-resistance improves, the strength and abrasion resistance of cellulose fabrics deteriorates, as much as 50 percent or more. As a result, it is necessary to reinforce cellulosic textiles with synthetic fibers which tend to counteract, to a degree, the loss in strength and abrasive resistance caused by the treatment of the cellulose fibers to render them wrinkle free. Another method of improving the strength of a treated fabric is to use more yarn per unit area of fabric.

A principal object of this invention is the provision of a process for curing cellulosic fibers which have been chemically treated for wrinkle resistance whereby their strength and abrasion resistance remain substantially unimpaired.

Yet another object of this invention is the provision of a process for curing chemically treated cellulosic containing fabrics utilizing microwave energy.

Still another object of the present invention is the provision of a method of manufacturing. press-free, crease-retaining clothing wherein the strength and abrasion resistance of said clothing is not substantially impaired.

Other objects, features and advantages of this invention will be apparent to those skilled in the art from the following detailed description and accompanying drawmgs.

IN SAID DRAWINGS FIG. 1 is a sectional, elevational view illustrating one form of the present invention;

FIG. 2 is also a sectional elevational view showing another arrangement for treating a garment in accordance with this invention; and

FIG. 3 illustrates a further form of this invention.

As indicated previously, oven curing of cellulosic textiles, which have been treated to impart creaseresistance thereto, can cause substantial loss in tear and tensile strengths as well as abrasion resistance. The reasons for such loss in these qualities are not precisely understood, it is believed that the uneven temperatures which occur with oven heating, where the cloth is heated from its outside surface to its inside, leads to non-uniform curing or perhaps to overcuring, especially overcuring of parts most subject to wear. To extend the cure throughout the fabric, the outside of the fabric may be over heated and thus damaged, especially those portions of a garment where there are folds, such as the cuffs of trousers, pleats in skirts, creases in trousers, etc.

It has been found, in accordance with this invention, that when the chemically treated cellulosic cloth is cured by microwave energy, the cured article has increased tear and tensile strength and also significantly greater resistance to abrasion than the same article cured by heat alone. As will be explained more completely, it is believed that the microwave energy heats the cloth or garment uniformly from the inside-out, as opposed to the non-uniform outside-in heating in a heat oven, which results in a uniform distribution of crosslinks and/or polymerization throughout the micro structure, thus preventing the large losses in strength and abrasion resistance while still imparting the desired crease resistant durable press properties.

In FIG. 1, a pair of trousers 10 which have been impregnated with an aqueous solution of a polymerizable resin is suspended in a microwave heating oven 12 by hanger 14 on rolling rack 16. These racks are moved through the oven sufficiently slowly to enable curing to occur during the interval of passage therethrough.

It has been found that when the chemically treated cloth is placed in the microwave oven, it is not adequately cured despite treatment times up to thirty minutes. It is not until the garment is insulated, as for example, by enclosure within a covering 18, which may be another cloth or some other material, or by placing in an environment, as described hereinafter, which enables the garment to retain much of the heat generated within the fabric by the microwave energy absorption and yet release its water vapor, that the garment can be satisfactorily cured in about 15 to seconds in an oven wherein the microwave frequencies are on the order of approximately 2.45 kilomegacycles per second. In general, the range of frequencies which may be used is that attributed to microwave processing, i.e., between about 800 megacycles and about 30 kilomegacycles, and the curing time is determined to a large extent by the moisture content of the cloth being treated.

At this point, it is advisable to distinguish microwave energy from other forms of electronic heating, namely, induction and dielectric. Induction heating operates by inducing a current in material by use of an alternating current in a coil surrounding the material, such as in a transformer. In dielectric heating, the material being heated is a part of the power generating electrical circuit, usually being placed between two parallel metal plates which makes the combination function as the capacitor in the circuit. Microwave heating is produced by the use of special oscillator tubes such as magnetrons and klystrons which generate very high frequencies, and heating with microwave energy isdone in an oven or other cavity, as described herein. The frequencies and wavelengths of microwave and dielectric heating are very different, and the Federal Communications Commission has set aside the following frequencies for ISMuse in dielectric heating and microwave processing which conform to the International Radio Regula tions (Geneva, 1959):

Dielectric l 3.5 megacycles/sec. 27 o. 40 do.

Microwave 915 megacycles/sec. t 25 mc./sec 2,450 do. i 50 do. 1 5,800 do. i 75 do. l7,925 do. i 75 do. 22,125 do. i125 do.

For further information on microwave processing and the other forms of electronic heating, reference may be made to"Microwave Heating in Freeze-drying, Electronic Ovens and Other Applications, David Copson, ,Avi Publishing Co., 1962.

The curing of the impregnated fabric in accordance with this invention is believed to establish crosslin'kages between the polyfunctional agent in the impregnating solution and the cellulose of the fabric, or to cause polymerization of the agent, or both of these mechanisms may occur. The cross-linkages are made to occur at an economically practical rate. 7

While covering of the cloth being treated provides a satisfactory environment to permit heat retention and water vapor release, another environment wherein such covering for each garment is not required is shown in FIG. 2, which is a cross-section of another embodiment of this invention. Since the curing of the garment or fabric within the oven, in accordance with this invention, should be such that the fabric does not lose heat to the environment of the oven, or at most loses a minimum of heat, the'interior of the microwave oven 12 can be filled with hot air from a hot air source 22. If the air within the oven which surrounds the garment is maintained at a temperature on the order of that required for curing the garment, covering of the garment is not required. Thus, the temperatures in the range between about 175 to about 500F. for the air surrounding the garment are generally satisfactory to provide the necessary insulation against loss of heat by the fabric, with the water vapor, of course, passing into the heated air.

The microwave heating of the material of the garment occurs substantially instantaneously throughout the garment and not on one surface, so that the environment of the garment being at an elevated temperature insulates the garment against loss of heat from its surface and thus permits curing to occur, but does not serveto deteriorate the surface of the garment which is exposed thereto within the time required to obtain an adequate cure. In order to prevent the occurrence of hot spots which can cause burns in the cloth being treated, it is preferable that the cloth or garment be kept in motion during the brief time required to effectuate curing. Alternatively, the microwaves can be stirred by a microwave stirrer, which is an arrangement provided with each microwave oven for causing multiple microwave reflections. Also, a combination of both techniques may be used. Although not clearly understood, it may be that curing occurs from the insideout of the fibers leaving these fibers more nearly like the untreated fibers to act as the wearing surface.

If it is desired to cure the cloth before it is formed into a garment, a continuous arrangement may be used such as shown in FIG. 3. Here the cloth is placed on a payout roll 24 which feeds through the microwave oven 26 and then out onto a take-up roll 28. The enclosure of the cloth to insulate the same against heat loss can occur by using two endless loops of cloth 30, 32. The cloth 30 is stretched over two rollers respectively 34, 36, and then through two applicator rollers 38, 40, which are within the oven to be in pressing contact with the cloth being fed from the payoff roll 24 to the takeup roll 28. Similarly, the endless loop of cloth 32 is supported between two rollers 42, which are outside the microwave oven, and also in contact with the cloth being cured by means of two rollers respectively 46, 48, which are within the oven. The speed of the respective rollers is adjusted so that the cloth travels through the oven during the interval required for obtaining proper curing. Alternatively, instead of using the two loops of cloth, hot air may be used, in the manner shown in FIG. 2, which has a temperature on the order required for curing.

Not only does the microwave curing arrangement described in accordance with this invention provide an improved product, but it also cures much more quickly than the present oven curing method. While oven curing usually requires between 5 to 25 minutes to cure cuffs or scams or any thick spot in the fabric, the curing time of the process of the present invention normally is on the order of about seconds.

It will, of course, be understood that the impregnated fabric may be insulated against heat loss from the surface thereof in ways other than set forth explicitly herein. By the same token, the covering 18 in the embodiment illustrated in FIG. 1 and the cloths 30 and 32 in FIG. 3 may be the indicated fabric as for example standard cotton twill or synthetic fibrous material such as blends of polyester and cotton, or other such material, including non-woven fibrous sheets, which is permeable to the water vapor occurring during curing, but will function as a barrier to heat to insulate the impregnated fabric.

Table I which follows provides someaverage data comparing the results of curing fabrics using microwave heating, in accordance with this invention, with the prior art method of thermal heating.

The chemicals used as the cross-linking agents were Warwick Textile Products Company Permafresh Reacltant 183 and Catalyst X-4. The chemical is dimethyol- 'dihydroxyimidazolidone:

Home The catalyst is Zn (NO 3 6 H O.

I The reactants come as solutions of undisclosed :strength and are then made up by dilution according to iWarwicks directions. The fabric is then padded @(soaked) in the solution, squeezed to damp dry, dried at moderate temperature and, in the prior art, would be cured at about 320 F. or higher.

Although such imidazolidone reactant performs satisfactorily, it is used only as an example of suitable reactants. Other available such cross-linking agents may be used such as DMEU, dimethylol propylene urea, carbamate and other glyoxal type reactants. Similarly,

,other known catalysts such as magnesium chloride,

zinc chloride, aluminum chloride and other metal salts, amine salts and free acid catalysts, may be used. The amount of reactant in the impregnating solution or dis- .persion may vary to a considerable extent and generally will be approximately the same as used in oven curingprocesses. Especially beneficial results have been obtained when the amount of cross-linking reactant is at least about percent by weight based on the total weight of the solution. The concentration of the catalyst will, of course, vary depending on the type of catalyst used; generally, the catalyst will be from about 0.1 to about weight percent, based on the weight of the cross-linking reactant.

Table 11 illustrates the difference in dry wrinkle recovery and flexing cycles between microwave and nonmicrowave heated 100 percent cotton, 80 X 80 squares of print cloth, which were padded with a 25 percent solution of Warwick 183 and catalyst. First one cloth Average Wrinkle Tear Average Recovery Strength Abrasion Range (Arbitrary Resistance x80 Print Cloth (Degrees) Units) (Seconds) Microwave Oven -Cured 270-295 205-250 4516 3.6:.5 Untreated -150 120 60:2 3.81.3

Wash & Wear Heavy Twill Rating Thermal Oven Cured 5 47:2 4.7:.3 Microwave Oven Cured 5 74:5 9.2:.9 Untreated 1+ 94:4 10.011

Table III is similar to Table 11 except that 136 X 68 square of Broadcloth (100 percent cotton) were used. Again, much better results were obtained with microwave heating each time.

High performance (wrinkle recovery) and stoll flex are obtained with the use of microwave energy.

TABLE 11 80x80 Print Cloth (100% Cotton) Dry Stoll Temper- Microwave Wrinkle Flex Treatment Time ature On Recovery Cycles Min F. Microwave oven and heat 1.5 265 No 240 257 do. 1.5 265 Yes 282 102 do. 2.0 265 No 264 do. 2.0 265 Yes 320 65 d0. 1.75 240 Yes 260 162 do. 2.0 240 No 232 331 do. 2.0 240 Yes 284 162 do. 25 240 No 264 308 do. 2.5 240 Yes 304 108 TABLE III 136x68 Broadcloth (100% Cotton) do. 2 220 Yes 290 909 do. 2 220 No 238 1307 do. 3 220 Yes 286 530 do. 3 220 No 254 963 do. 2 240 Yes 302 296 do. 2 240 No 238 1196 do. 3 240 Yes 302 386 do. 3 240 No 252 l 143 do. 4 200 Yes 300 675 do. 4 200 No 220 1267 Standard Heat Oven 10 310 No 300 16 do. 18 310 No 316 10 do. 5 310 No 46 To demonstrate further the significant improvement of the present invention, Tables 4 and 5 which follow show the comparative characteristics of broadcloth and poplin processed in accordance with this invention and conventional oven heating. The broadcloth and poplin fabrics were impregnated with an aqueous solution containing 20 weight percent of the previously described Permafresh 183 and 4 percent zinc nitrate catalyst. The materials were then sewn into cuffs and given sharp creases on a garment press. After conditioning at 65 percent relative humidity, the cuffs were cured, with the conventional curing being done in an oven at 320 F., while the microwave curing was undertaken in a microwave oven at 850 watts of power. The microwave oven was set to give a fabric surface temperature of about 200 F. After processing, the cured cuffs were attached to the legs of trousers and subjected to repetitive standard wash and dry cycles.

In Table 4, the characteristics of the broadcloth cuffs are shown, while Table shows the characteristics of the poplin cuffs. In the case of Fabric B, the impregnating solution contained about 25 weight percent of Permafresh 183 and 5 percent of zinc nitrate catalyst.

.The results set forth in Table 4 show that, compared to conventionally cured broadcloth fabrics, the microwave cured cuffs had slightly higher tearing strengths and Stoll flex ratings, as well as approximately to percent higher tensile strength. Also, the microwave cured cuffs withstood 4 to 5 times the number of wash and dry cycles than did the oven cured cuffs. Likewise, Table 5 shows that, compared to oven cured poplin cuffs, the microwave cured cuffs had significantly higher tearing strengths and Stoll flex ratings, as well as about percent greater tensile strength. The microwave cured cuffs were quite superior in the wash and dry test, withstanding 2% to 6 times the number of cycles.

ing a water vapor pervious insulating material between the fabric surface and the ambient atmosphere or directly contacting the fabric surface with air at elevated temperatures prior to beginning said treatment with microwave energy.

2. The method of claim 1 in which said cross-linking agent is dimethyl dihydroxy-imidazolidone.

3. The method of claim 2 in which said impregnating solution contains at least about 20 weight percent of said cross-linking agent.

4. The method of claim 1 in which said impregnated fabric is formed into a garment prior to curing.

5. The method of claim 1 in which said fabric material is continually moved while microwave energy is applied thereto.

6. The method of claim 1 in which the microwaves are continually stirred while said microwave energy is applied to said fabric.

7. The method of claim 1 in which said loss of heat from said fabric is compensated by placing said fabric in an environment in which the fabric surface is directly contacted with heated air at a temperature on the order of the curing temperature for said fabric.

8. The method of claim 7 in which the temperature of said environment is between about 175 to about 500 F.

9. The method of claim 1 in which said loss of heat TABLE IV 1. A method of improving the crease resistance of a textile material wherein a cellulosic containing fabric impregnated with an aqueous solution of a cellulosereactive cross-linking agent is subjected to treatment with microwave energy at a frequency within the range of from approximately 800 megacycles per second to about kilomegacycles per second to elevate the fabric temperature to the curing temperature and heat loss from the fabric surface occasioned by the evaporation of water therefrom during the microwave energy reaction promotion iscompensated for by either interpos- Number Tensile Properties (ufter 25 wash cycles) of Wash- Non- Dry Cycles Tear Tensile Conditioned Conditioned Cure Time to Holes (W) Stoll Strength Work Extension Extension Fabric (min) Average Range (grams) (cycles) (lbs) (in-lbs) ("/1 Broadcloth Oven Cure 7.5 at 320F 3 2-4 320 160 35 2.5 8.9 6.7 B 2 2 300 130 34 2.5 8.8 6.9

Microwave Cure A 3.0 ll 9-44 400 220 4l 3.3 9.7 6.7 B l4.5 11-17 410 250 4] 3.7 9.9 7.0 A 3.25 l4 l4 390 230 43 3.8 l0.l 7.l B 8 8 380 220 38 2.8 9.8 6.7 A 3.5 15 l2-l7 400 260 42 3.5 11.1 7.3 B 1] 6-15 380 230 38 2.8 10.2 6.8

Poplin Oven Cure A 10 at 320F 2 23 530 I20 59 3.9 8.3 6.0 B 2 2 500 85 59 3.9 8.6 6.2

Microwave Cure A 2.5 10 7-14 700 250 77 6.2 9.7 6.0 B 12' 8-16 650 250 74 6.1 9.4 7.0 A 2.75 12.5 5-20 720 v 290 5.3 9.3 5.6 B 12.5 6l9 700 370 70 5.0 9.7 5.8 A 3.0 5 2-l0 650 290 70 4.9 9.5 5.9 B 13 8-22 670 290 73 5.4 9.8 6.2

H we cla m: from sa1d fabric 15 compensated by enclosing said fabric within said material prior to application of said microwave energy.

10. The method of claim 9 in which said reactive cross-linking agent is dimethyol dihydroxyimidazoli-' done.

11. The method of claim 10 in which said impregnating solution contains at least approximately 20 percent by weight of said reactive cross-linking agent.

12. A cellulosic containing fabric of improved strength and abrasion resistance produced by the method of claim 1. 

1. A METHOD OF IMPROVING THE CREASE RESISTANCE OF A TEXTILE MATERIAL WHEREIN A CELLULOSIC CONTAINING FABRIC IMPREGNATED WITH AN AQUEOUS SOLUTION OF A CELLULOSE-REACTIVE CROSS-LINKING AGENT IS SUBJECTED TO TREATMENT WITH MICROWAVE ENERGY AT A FREQUENCY WITHIN THE RANGE OF FROM APPROXIMATELY 800 MEGACYCLES PER SECOND TO ABOUT 30 KILOMEGACYCLES PER SECOND TO ELEVATE THE FABRIC TEMPERATURE TO THE CURING TEMPERATURE AND HEAT LOSS FROM THE FABRIC SURFACE OCCASIONED BY THE EVAPORATION OF WATER THEREFROM DURING THE MICROWAVE ENERGY REACTION PROMOTION IS COMPENSATED FOR BY EITHER INTERPOSING A WATER VAPOR PERVIOUS INSULATING MATERIAL BETWEEN THE FABRIC SURFACE AND THE AMBIENT ATMOSPHERE OR DIRECTLY CONTACTING THE FABRIC SURFACE WITH AIR AT ELEVATED TEMPERATURES PRIOR TO BEGINING SAID TREATMENT WITH MICROWAVE ENERGY.
 2. The method of claim 1 in which said cross-linking agent is dimethyl dihydroxy-imidaZolidone.
 3. The method of claim 2 in which said impregnating solution contains at least about 20 weight percent of said cross-linking agent.
 4. The method of claim 1 in which said impregnated fabric is formed into a garment prior to curing.
 5. The method of claim 1 in which said fabric material is continually moved while microwave energy is applied thereto.
 6. The method of claim 1 in which the microwaves are continually stirred while said microwave energy is applied to said fabric.
 7. The method of claim 1 in which said loss of heat from said fabric is compensated by placing said fabric in an environment in which the fabric surface is directly contacted with heated air at a temperature on the order of the curing temperature for said fabric.
 8. The method of claim 7 in which the temperature of said environment is between about 175* to about 500* F.
 9. The method of claim 1 in which said loss of heat from said fabric is compensated by enclosing said fabric within said material prior to application of said microwave energy.
 10. The method of claim 9 in which said reactive cross-linking agent is dimethyol dihydroxyimidazolidone.
 11. The method of claim 10 in which said impregnating solution contains at least approximately 20 percent by weight of said reactive cross-linking agent.
 12. A cellulosic containing fabric of improved strength and abrasion resistance produced by the method of claim
 1. 